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Abstract
Objective: To ascertain the epidemiology of ankle injuries in elite youth football.
Design: Retrospective analysis of prospectively collected injury data from English Football Association (FA) academies.
Setting: Forty-one FA football academies, between 1998 and 2006.
Participants: For the complete seasons studied, a total of 14 776 players was registered from U9 to the U16 age category, a mean of 2463 players per year. All ankle injuries of sufficient severity to miss 48 h or more of training were studied, 2563 injuries in total.
Main Outcome Measure: The incidence and burden of ankle injuries in this population and factors associated with injury.
Results: There was a mean incidence of one ankle injury per player per year, and a mean of 20 training days and two matches were missed per ankle injury. Increased injury rates were seen in older players, in competition and later in each half of match time. Peaks in injury were observed early in the season and after the winter break. In competition, more injuries were associated with a contact situation than in training. Eighty-eight injuries (3.4%) required a lay-off of 3 months or more and in 18 (0.7%) cases the player failed to return to training. In total, 52 290 training days and 5182 match appearances were lost through ankle injury. The majority of injuries were sprains, but more severe injuries occurred accounted for 3.9% of the total.
Conclusions: Ankle injuries are common in young football players and are often severe, with prolonged loss of training time. This has potential far-reaching implications, both on and off the field.
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Soccer is a complex contact sport, associated with high levels of injury, in both professional1 and amateur players,2 as well as the youth game.3 4 5 6 7 8 9 10 11 In the professional adult population, previous work has demonstrated injuries to almost all players over the course of a season.1 Of these injuries, the foot and ankle are commonly affected, with a reported proportion of between 11%11 and 18%1 of all injuries. This may lead to a marked loss of training and competition time. Although the majority of ankle injuries are “sprains”,11 the spectrum encompasses soft tissue injury through isolated fracture to joint disruption.
The English Football Association (FA) set up football academies associated with major professional clubs in 1998, to improve the development of young players. However, with greater emphasis upon participation at a younger age in sport, adolescents are subjecting the immature skeleton to prolonged and intensive repetitive loading. This may have serious consequences, particularly in the event of injury. As a result of the ongoing growth of the individual, those injuries resulting in any growth disturbance may cause progressive and permanent impairment.12 Although skeletal maturity does not appear to alter injury risk, the patterns of injury may differ with changing maturity.3
Injuries in youth sports are of concern for many reasons. In young people, severe injuries may have a lifelong effect on an individual, including sporting and work activities and employment, with a cost to that individual and society as a whole. Although growth allows for great adaptability to demands placed on the tissues, this ability to adapt to applied loads may at times be exceeded by demand, resulting in overuse injury.13 Recognition of these factors has led to limits being placed on the duration, frequency and nature of training and competitive sports. In the FA academies, the frequency of training increases with age (twice per week to age 17 years), and only seven-a-side matches are played under the age of 13 years.
Although not as great as in the professional game, the incidence of injury in youth players is still of concern, estimated at 0.63 injuries per youth player per year in Denmark.6 However, more recent work in the FA academies demonstrated 0.4 injuries per player per year,4 whereas in the setting of a national centre for youth football, an injury rate of 2.2 injuries per player per season (4.8 per 1000 h exposure time) has been documented.3 On average, the proportion of these injuries involving the ankle has been estimated to be up to 23%.1 4 6
Previous work in professional football has found that 83% of players with sprains returned to play within one month11 but the consequences of ankle injuries can be chronic in nature. In one study, 14 of 19 athletes with an isolated ankle ligament sprain had ongoing symptoms at a mean of 29 months follow-up.14 Those cases that are slow to return to function may represent a more serious, undiagnosed pathology. For example, osteochondral fractures have been noted in 6.5% of ankle sports-related “sprains”.15 The majority of studies have studied the adult skeleton, but few data exist on the impact of intensive training, such as is seen in an academy setting, upon the immature skeleton.
In this study we have examined the demographics of ankle injury within the setting of FA academies, with an emphasis upon the mechanism and timing of injury, with a view to elucidating the risk factors for prolonged disability.
Methods
We have collated and analysed prospective data from 40 FA academy injury audit databases between 1998 and 2006. Under FA guidance, player injuries were recorded at the academies prospectively from November 1998 to January 2006. These data were collected at club level by academy medical personnel and submitted to the FA on a weekly basis. Consent for this information to be used was completed by the player or legal guardian, according to age. Injuries were defined by time loss of 48 h or more from training or competition, for all age groups (9–19 years). Absence through illness or injuries sustained outside of the academy setting was not recorded.16 17 18
The presence of medical staff (physiotherapist) is required at matches by the FA rules. Treating academy medical personnel (physiotherapist or doctor) recorded the injuries and submitted the data on a standardised proforma, following a briefing day and the issue of guidance notes. Data recorded included player data, the mechanism, timing and nature of injury, the activity leading to injury, the date of return to unrestricted training (the end of rehabilitation), failure to return to training, any further investigations or surgical interventions and the number of matches missed. Re-injury was defined as a further injury of the same nature to the same anatomical location and side as previously, irrespective of timing. The forms were returned when the player had returned to full training/competition. The questionnaires were collated by the FA, and the data were stored using the SPSS statistical software package.
Ethical approval for the use of these data in this study was obtained from Bath University Ethics Committee.
The number of players registered at the end of each season, by age group, was obtained from the Premier League, who coordinate the academy league up to U16. No such data were available for the older age groups. The number of players registered at the end of each season was taken as an estimate of the numbers participating through the year. For the complete seasons during the study period, a total of 14 691 players was registered up to the U16 age category, a mean of 2463 players per year. The distribution of player numbers by year and age group is shown in table 1.
Numbers of players registered by year and age group
For this study, only those injuries pertaining to the ankle were analysed, selected by the coding of the injury location from the dataset. All such ankle injuries were included in the analysis. Descriptive analysis was performed for the data collected, along with further analysis of more severe injuries (fracture, dislocation, chondral or osteochondral injury, ligament rupture, ankle instability, loss of more than 3 months training, surgical intervention, or failure to return to training). Recommendations regarding the definition of injury severity have been made.16 17 18 However, we have defined severe injuries to include both those diagnosed with a severe pathology and those with prolonged time lost.
The data were analysed using the SPSS statistical software package. Descriptive and comparative data were analysed, using χ2 tests when appropriate to investigate differences, and Student’s t tests to compare means. One way analysis of variance (ANOVA) was used for categorical data. Regression analysis was used for continuous variables and ANOVA for categorical data. The significance level was set at p<0.05.
Results
In total, 13 662 injury episodes were recorded between November 1998 and February 2006, of which 2563 were ankle injuries (19%). Data were therefore available for complete seasons between 1999–2000 and 2004–5. In total, 88 injuries (3.4%) were severe enough to result in 3 months or more lay-off and 18 (0.7%) failed to return to training. In total, 52 290 training days and 5182 match appearances were lost through ankle injury in those injuries recorded (ie, missing two or more days training). The distribution of training days lost is shown in fig 1. The mean time loss per ankle injury was 20.4 days and the mean number of games missed per ankle injury was two. Given the mean number of players registered per year (2463), there was a mean incidence of one ankle injury per player per year, and a mean of 3.5 training days and 0.35 matches were lost per player per season through ankle injury.
Distribution of number of training days lost through ankle injury.
There was a clear trend towards an increasing incidence of ankle injury with increasing age group across the cohort as a whole (fig 2). The age group was not recorded in 77 cases (3%). There was no significant change in ankle injury year by year. Up to U16, the correlation coefficient for the relationship between age group and injury incidence was 0.98 (p<0.001 by one-way ANOVA between injury incidence and age group).
Ankle injury incidence by age group.
The injury was to the dominant ankle in 61.6%, the non-dominant in 35.1% and both in 2.7%. The right ankle was injured in 56.7% of cases and the left in 43.3%.
A total of 473 injuries (18.5%) underwent radiological investigation: plain x ray in 377; bone scan, computed tomography (CT) or magnetic resonance imaging (MRI) in 122. Surgery or other invasive procedures were performed in 51 cases (2%).
The injury diagnoses are listed in table 2. Sprain was the most common diagnosis (1621 cases, 63%). Fractures, ligament ruptures, chondral or osteochondral injures, or ankle instability were diagnosed in 99 cases (3.9%). In total, 1383 (54%) injuries were recorded as affecting the anterior tibiofibular ligament.
Injury diagnoses
One hundred and one cases (3.9%) represented a re-injury of the ankle. There was no significant association between re-injuries and more serious diagnoses, mechanism of injury, training time or matches missed, although re-injury was more likely to be investigated by MRI.
The Premier League academy season runs from August until early May. There was a peak rate of injury at the beginning of the season and a further peak after the winter break (fig 3), with decreasing numbers of injuries towards the middle and end of season. The month was not recorded in 34 cases (1.3%). There was no significant relationship between more severe injuries or time lost in training with the month of injury. Injuries were sustained more frequently in competitive play between September and April (except January) (ANOVA p<0.001).
Ankle injury frequency by month.
The nature of activity leading to injury is shown in table 3. The majority of injuries occurred in competitive games. Table 3 also describes training activities undertaken leading to injury, but no data were available on the proportion of time spent in these activities.
Activity at time of injury
The majority of injuries were sustained in competition (n = 1341, 52.3%). There was a statistically significant increase in injuries investigated by x ray sustained in competitive play (222 in competition vs 155 in other activities; p = 0.002). However, although there was a trend towards more serious diagnoses in those injuries sustained in competition, this did not reach statistical significance (p = 0.097). Equally, there was no significant increase in the loss of more than 3 months training, failure to return to training, time training or matches lost, between injuries sustained in competitive play and others.
With regard to competitive games, it was possible to ascertain the timing of injury in 1128 cases. A significantly greater frequency of injuries was observed in the second half of play, with more injuries occurring in the middle and late intervals of each half than early in each half (fig 4). There was no significant association between the severity of injury, time training or matches missed between first and second half injuries.
Ankle injury frequency by match period.
The mechanism of injury is recorded in table 4. Overall, 1324 (51.7%) injuries were associated with a contact situation (tackled, tackling, collision, kicked or other contact). During competition, 856 injuries were sustained in a contact situation (65%), whereas in non-competitive situations there were 468 contact injuries (37%); p<0.001. Four of the 18 injuries in players who subsequently failed to return to training were sustained by a contact mechanism, a significantly higher proportion than those returning to training (p = 0.04). Contact injuries were more likely to affect the dominant limb. Whereas there was no significant relationship between contact injuries and more severe diagnoses, training time or matches missed, there was a trend towards more serious diagnoses following contact injuries, although it was not significant. This is corroborated in the observation that injuries sustained in contact situations were significantly more likely to be investigated by x ray (p = 0.03).
Mechanism of injury
Several factors were found to be significantly related to the loss of more than 3 months training. These included injury to the dominant limb (p<0.001), more serious diagnoses (fractures, dislocations, ligament ruptures; p<0.001), investigation by x ray, bone scan, CT and MRI (p<0.001) and surgical intervention (27/88; p<0.001). No such relationship was seen by playing position, or by contact mechanism.
Overall, there was a significant relationship between greater severity of injury (more than 3 months time lost) and injury to the dominant limb, more serious injuries (fractures, dislocations, ligament ruptures), investigation by bone scan, CT and MRI and surgical intervention (27/88), but not with playing position or contact mechanism. Similarly, the more serious diagnoses of injury were more frequent in the dominant limb and 20 of 99 cases (20%) underwent an invasive procedure.
Discussion
Our study has demonstrated the high incidence of ankle injuries in elite youth soccer. There was a mean incidence of one ankle injury per player per year and the mean time loss per ankle injury was 20.4 days. Ankle injuries increase in incidence with age group. We found more injuries in competition, when a contact mechanism is most commonly seen; whereas in training non-contact mechanisms were more common. Eighty-eight ankle injuries (3.4%) were severe enough to result in 3 months or more lay-off and 18 (0.7%) failed to return to training.
Studies of injuries in football have been reviewed by Inklaar.7 Various methods of recording injury incidence are used in the literature and injury definition varies, as does the assessment of severity. A consensus on these factors has been outlined in the UEFA model.18 Recommendations include recording individual exposure times to allow the expression of injury rate per 1000 h, data collection over whole seasons and a definition of injury as the absence from a training session or match. However, our data collection commenced before these recommendations were published and we defined injury as time loss of 48 h. Although this procedure may lead to the non-recording of more trivial injuries,16 it has been used in previous work.3 4 As with previous work on data collected in this population4 we report on the numbers and proportions of injuries, with an estimation of the population at risk.
Many studies have focussed on injuries in youth football players. Settings have included tournaments,5 single seasons,6 7 8 or single teams.9 10 Hawkins and Fuller1 have studied injuries within professional teams and youth teams alongside them, and Price et al4 examined the dataset used for this study over two seasons. Le Gall et al3 examined a 10-year cohort of elite youth players (528 players). In these works, ankle injuries have represented a significant and consistent proportion of the injury burden, between 17% and 23%.1 3 4 6 Our work is consistent with these estimates, finding ankle injuries to represent 19% of the total. However, we are not aware of other specific studies of ankle injuries in this setting. We believe this study represents the largest series of ankle injuries in youth football players.
Our results demonstrate that in elite youth soccer, injury rates are generally seen to increase with age. This finding is in accordance with the observations of previous studies of injuries in youth football.1 3 4 6 9 10 This has been ascribed to factors including increasing time in training and competition, increasing speed, strength and mass and greater competition.4 Le Gall et al19 have also examined injuries in relation to skeletal maturity, finding no overall relationship with the incidence of injury. In our setting of the FA academies, only seven-a-side games are permitted up to the age of 13 years, which may relate to the lower injury rate in younger players.
Several studies on youth football injuries in general1 3 4 5 14 have found there to be a greater number of injuries in competition. In those studies in which the incidence per 1000 h exposure is given1 3 the rate of injury in competition is significantly greater, given the relatively short time spent in competition compared with training. Whereas we cannot calculate injury incidence in our work, we have similarly found increased numbers of injuries in competition (52%), which would suggest a higher rate of injury.
Woods et al11 prospectively studied ankle injuries over two seasons in 91 professional English teams. Many of their findings reflect ours in the youth population, with more injuries occurring in competition. We have noticed slightly fewer contact injuries in the youth population overall than in their series (52% compared with 59%). However, no differentiation is made between contact injuries sustained in competition and training; we found significantly more contact injuries in matches. More contact injuries in the adult game may represent increased contact energy (greater speed, mass and aggression).4 Alternatively, it has been suggested that poorer endurance, coordination and skill in the youth game may be a factor in the increasing non-contact injury rate towards the end of each half.1 4 20 A significant trend towards ankle injury towards the end of each half has been described in the amateur adult game.2 We similarly observed a trend towards increasing injury rates towards the end of each half of match play. In a comparison of adult and youth teams at various levels, an increased rate of injury was seen in both youth teams and lower league teams compared with professionals.21 The effect of a relative lack of skill and conditioning was suggested as a factor, along with a higher level of medical care in professional teams. In the amateur game, ankle injuries were seen to peak at the beginning of the season,2 and in a comparison of youth and professional games, adult injuries were seen to decrease through the season, whereas youth injuries peaked early and late.1 It was again suggested that differences in overall conditioning and training may have played a role in the late peak.
The injury pattern through the year was similar in our study to the previous work on the FA academies,4 with peaks in injury rates early season (after the summer break) and after the winter break. Other work has not demonstrated an increased incidence following breaks.3 We have found the numbers of injuries sustained in training to be greater than in competition in August and January after these breaks. The effect of return to training and play after a break may therefore be a greater factor in injury than prolonged periods of training and play at the same level. However, it is possible that environmental factors such as hard ground in the summer and wet ground in the winter may play a role.
What is known on this topic
Injuries in elite youth football have an incidence less than that in adult elite football, but the incidence increases with age.
Ankle injuries constitute up to 23% of these injuries.
What this study adds
The rate of ankle injuries increases with age group.
These injuries are most commonly sustained in competition through a contact mechanism, and peak after summer and winter training breaks.
Whereas sprains are the most common injury, other more serious pathologies can occur.
Measurement of the extent of an injury problem, its aetiology and mechanism, have been described as key steps in the development of preventive strategies.22 Several studies have examined the risk factors (and thus suggested possible preventive strategies) for football injuries. In a prospective study of Czech players,23 risk factors for injury included poor self-rated skill, pre-existing joint pain, poorer reaction times, tiredness before games and previous injury to the same area. Preventive strategies including improved rehabilitation for old injuries and work on endurance and skill were suggested. Some of our findings, such as increased injury late in each half, and injury early season and after the winter break are in keeping with the suggestion of poor conditioning as a risk factor for injury.
Self-reported previous injury as a risk factor for re-injury has been examined in more detail in youth players.24 In particular, two or more previous ankle injuries led to an eightfold increased risk of further ankle injury. In a population of female youth players,25 lower pre-season functional scores were observed in those with previous injury and a significantly increased risk of re-injury (proportional to the number of previous injuries). Lower functional scores were predictive of injury, suggesting inadequate rehabilitation, and the use of screening questionnaires to target remedial rehabilitation to prevent injury. Other work has confirmed previous injury as a risk factor in the adult amateur and youth game.2 26 In terms of re-injury, we defined this as those of the same nature to the same location and side as a previous injury. It has been recommended that a time limit be placed on the definition of re-injury to reduce recall bias, but even so our figure of 3.9% compares favourably with the adult professional population at 9%.11 This is encouraging, and may represent more complete rehabilitation and less pressure to return early in comparison with adults. Preventive strategies have been prospectively studied in only a couple of works,27 28 but the role of adequate rehabilitation and improved conditioning, skill and coordination has been outlined, particularly for more minor injuries.28
The overall burden of ankle injuries occurring in these young players is high. In total, 52 290 training days and 5182 match appearances were lost. The mean time loss per ankle injury was 20 training days, similar to the mean time loss though all injuries in previous work;4 this time loss was estimated at 6% of the season. In our cohort sprains represented the majority of injury diagnoses, 63%. This is similar to other youth series (72% in the series of Price et al)4 and adult professional series (67%).11 In themselves, the number of sprains occurring in young players is of concern. Although 83% of professionals returned to play within one month,1 one study has suggested that up to 74% of sports-related ankle sprains (in the adolescent and adult population) have symptoms over one year later.14 However, of the 19 injuries in this study, three failed to return to their original sport and the mean return to sport in the remainder was 13 weeks. It seems unlikely that the true diagnosis in many of these cases was simple sprain. In a study of ex-national players in Denmark, 33% of previously injured ankles showed radiographic signs of osteoarthritis at a median 25-year follow-up, but so did 17% of uninjured ankles. However, the injury history was self-reported and some previous injuries may have been forgotten.29 It is possible that those injuries with ongoing symptoms, and later degenerative problems, have missed more serious pathology; osteochondral fractures have been noted in 6.5% of ankle sports-related “sprains”.15
Of more concern are the severe injuries. Eighty-eight injuries (3.4%) were severe enough to cost 3 months training or more and 18 (0.7%) failed to return to training. Fractures, ligament ruptures, chondral or osteochondral injures, or ankle instability were diagnosed in 99 cases (3.9%), of whom 20 underwent surgery. We also noted a non-significant trend towards more severe injuries in competitive play, and the finding that more injuries in competition were investigated by x ray suggests higher energy, more subjectively severe injuries. It is these more severe diagnoses that lead to increased loss of training and playing time in young players, which will impact on the likelihood of a future professional career, but may also lead to permanent impairment and disability, impacting on other future employment.
Although we have recorded a larger series of ankle injuries, our study has a number of limitations. Our definition of injury differs from the UEFA model,18 in that injuries were defined as time loss of 48 h or more (rather than 24 h), thus we may have underrecorded more minor injuries. A small proportion of the data was incomplete. The data were recorded prospectively by a number of health professionals from different backgrounds, thus the clinical diagnoses made in the same situation may vary. Investigation results were not recorded, which may have impacted on the final diagnosis. Further prospective work is underway to study in detail the more severe of these injuries. In the study of Price et al4 of data from this source, the time spent in training and match play was not assessed and we can therefore only present the numbers of injuries rather than the rate per hours of exposure. However, we have obtained an estimate of the numbers of players in the academy teams to enable an estimation of the injury rate.
This study represents a large series of ankle injury data from a youth football population. We have found a high incidence of ankle injury, which appears to increase with age. The risk is greater in the latter end of each half of play. We believe that this corresponds to tiredness and possible loss of muscle coordination. The emergence of more sophisticated motion analysis30 offers the possibility of examining factors such as changes in motion patterns associated with fatigue later in each half of play.
Time spent training and playing in the academy setting is limited, particularly in younger players, but it may be that improved endurance fitness and neuromuscular coordination will help improve the injury incidence. Further work is needed to elucidate the risk factors associated with more severe injuries, the nature of their diagnoses and their outcome.
REFERENCES
Footnotes
Funding This study was internally funded by the Football Association. No sources of external funding were received.
Competing interests None.
Ethics approval Ethics approval for the use of these data in this study was obtained from Bath University Ethics Committee.